What voltage drop is acceptable for solar?

Aim for 1–2% on DC circuits; 3% maximum.

What current should I use?

The string's Imp, or inverter input current on battery circuits.

Why does 12 V suffer more?

Low voltage means high current, so losses climb fast.

What wire for solar panels?

10 AWG PV wire for most residential strings.

Why does 12 V suffer more drop?

The same power needs much more current.

What size cable from battery to inverter?

It depends on current — often 2/0–4/0 AWG at 12–24 V.

Solar wire voltage drop calculator

Cable length, current, voltage and conductor size: you get drop in volts and percent, power lost and the minimum size for your target.

Voltage drop

2.89 %

Voltage drop1.39 V
Voltage drop (%)2.89 %
Power lost in the cable13.89 W
Minimum size for target drop16 mm²

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How it's calculated (visible formula)

VD = 2 × L × I ÷ (γ × A); loss = I × VD; A_min = 2 × L × I ÷ (γ × V × VD%)

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Measure one-way cable length between the two devices.
Enter the run's working current.
Enter system voltage at that point.
Enter conductor size.
Compare the drop with the target and resize.

Worked example: 66 ft at 10 A and 48 V with 6 mm² (≈ 10 AWG)

VD = 2 × 20 × 10 ÷ (48 × 6) = 1.39 V
2.9%
For 1.5%: ≥ 11.6 mm² → 16 mm² (≈ 6 AWG)

→ 2.9% drop (14 W lost).

Common mistakes

Forgetting round trip (× 2).
Using short-circuit current for drop.
Thin cables between battery and inverter.

Pro tips

Use PV wire rated for UV and outdoor use.
Battery-to-inverter runs carry high current — keep them short and heavy.
Fuse each string properly.
Torque connectors — a bad joint heats more than the wire.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

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FAQs

What voltage drop is acceptable for solar?: Aim for 1–2% on DC circuits; 3% maximum.
What current should I use?: The string's Imp, or inverter input current on battery circuits.
Why does 12 V suffer more?: Low voltage means high current, so losses climb fast.
What wire for solar panels?: 10 AWG PV wire for most residential strings.
Why does 12 V suffer more drop?: The same power needs much more current.
What size cable from battery to inverter?: It depends on current — often 2/0–4/0 AWG at 12–24 V.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.